Blood flow oscillations (BFO) is an emergent biomarker to assess micro vascular dysfunction and risk for pressure ulcers. Research studies have demonstrated that BFO is regulated by endothelial metabolic, sympathovagal neurogenic, and vascular myogenic control mechanisms. By assessing the changes of BFO, tissue viability and ischemic injury can be further quantified. Such knowledge is needed to early detect pressure ulcers as well as to assess efficacy of preventive interventions. However, there is no definition of good or poor tissue viability based on the values of BFO. We propose to quantify the changes of BFO associated with aging and physical inactivity to investigate the role of micro vascular dysfunction in developing pressure ulcers. Such information can be used to early detect pressure ulcers in the elderly population. The long-term goal of this study is to develop methods for early detection of pressure ulcers based on the analysis of linear and nonlinear properties of BFO and then to use the methods to assess the efficacy of preventive interventions on enhancing tissue viability in older adults. The objectives of this study are to quantify the changes of linear and nonlinear dynamical properties of BFO in response to aging, inactivity, and ischemia (soft tissue status before stage 1 pressure ulcers) in older people with various levels of risk for pressure ulcers. Specific aim 1 is to investigate the effects of aging and physical inactivity on tissue viability through analysis of linear and nonlinear properties of BFO. Linear analyses include wavelet and Hilbert transforms and empirical mode decomposition. Nonlinear analyses include Hurst exponent, detrended fluctuation analysis, correlation dimension, sample entropy, and Lyapunov exponent. This study will establish the basic understanding of linear and nonlinear properties of BFO and their relationships with risk for pressure ulcers. Specific aim 2 is to examine whether the changes of linear and nonlinear properties of BFO can be used to predict pressure ulcers. Currently we hypothesize that a decline of linear and nonlinear properties of BFO is associated with the risk for pressure ulcers. We will measure BFO in a consecutive 24-week period to capture the changes of BFO from normal, declined, pre stage 1 pressure ulcers, and onset of pressure ulcers stages. If successful, we will be able to use the information to assess whether soft tissue is under good viability, ischemia, or pre-stage 1 pressure ulcer phases. PUBLIC HEALTH RELEVANCE: This study will establish the foundation to develop assessment tools based on linear and nonlinear properties of blood flow oscillations that will guide clinicians for the early detection of pressure ulcers in older people with physical disabilities.